Provided are a stirring device which stirs, by means of sound waves, a liquid dispensed in a container, an automatic analyzer, and a stirring method. A stirring device (20) is provided with: a first sound wave generating element which is disposed to a container (7) and outputs sound waves which detect the quantity of a liquid (L); a second sound wave generating element which outputs sound waves which stir the liquid; a drive control unit (31) which controls drive of the first and second sound wave generating elements; a frequency monitor (34) which monitors the frequency of the sound waves outputted from the first sound wave generating element; and a liquid quantity determining section (32) which determines the liquid quantity, based on the change of the sound wave frequency monitored by the frequency monitor. The drive control unit controls drive of the second sound wave generating element, based on the liquid quantity determined by the liquid quantity determining section.